Fix memory leak in t-mpi-point test

* tests/t-mpi-point.c (basic_ec_math, basic_ec_math_simplified): add
calls to gcry_ctx_release() to free contexts after they become unused.

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Specify stack_burn for SHA256 cipher

* cipher/sha256.c (sha256_init): fill stack_burn information for SHA256
cipher, which otherwise will contain random value.

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Add a simple PKCS#1 padding mode

* cipher/pubkey.c (sexp_data_to_mpi, pkcs1_encode_for_signature_simple):
handle s-exp like (data (flags pkcs1) (value xxxxx))

Allow user to specify (flags pkcs1) to enable pkcs1 padding of raw value
(no hash algorithm is specified). It is up to the user to verify that
passed value is properly formatted and includes DER-encoded ASN OID of
the hash function.

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Merge branch 'master' of github.com:lumag/libgcrypt-gost